ABSTRACT Breast cancers are newly diagnosed in more than 200,000 American women annually. Breast cancer mortality is generally due to the occurrence of metastasis. The cyclooxygenase-2 enzyme (COX-2) is highly expressed in breast cancer and contributes to metastatic success. Selective COX-2 inhibitors limit breast tumor growth and metastasis, however, recently identified cardiac toxicities associated with global COX-2 inhibition prompted us to take a novel approach to target the COX-2 pathway. The chief COX-2 product in tumors is prostaglandin E2 (PGE2) which mediates biological effects by binding to each of four EP receptors (EP1-4). We have demonstrated that two of these receptors, EP1 and EP4, play opposing roles in modulating breast tumor metastasis. Pharmacologic antagonism or genetic silencing of EP4 reduces metastatic potential; antagonism of EP1 increases dissemination. We hypothesize that EP1 acts as a metastasis suppressor and that expression is decreased in women likely to develop disseminated disease. Furthermore, that EP1 controls metastasis by a mechanism dependent on Natural Killer cells. We will carry out the following Specific Objectives to test these hypotheses: Using a unique collection of early stage breast cancer specimens for which longterm survival is known we will (1) determine the relationship of EP1 expression to behavior in clinical breast cancer. Using a preclinical model, we will (2) determine the functional significance of EP1 and determine the contribution of Natural Killer cells to EP1 function. EP1 and other G-protein coupled receptors may mediate cellular effects in the nucleus as well as the plasma membrane. We will (3) identify the cellular location and function of EP1. Since all EP receptors bind the same ligand, altering the function of one receptor may adversely affect other EP receptor functions. We will (4) identify strategies to restore the balance of the protective (EP1) and the pro-metastatic (EP4) receptor. Potential Impact on Veterans Health Care: Breast cancer incidence increases with age and since the mean age of Veterans is 58, breast cancer will impact a significant number of Veterans in the coming years. The current Veteran population is approximately 26 million; of these, nearly 200,000 female Veterans will be diagnosed with breast cancer. Therefore, reduction in mortality from metastatic breast cancer would have a significant social and economic impact on Veterans Health Care. These studies will establish a rationale for modulating EP1 expression and function to achieve this goal. PUBLIC HEALTH RELEVANCE: Relevance of the proposed work to the VA patient care mission. Cancers of the breast are newly diagnosed in nearly 200,000 Americans each year. Breast cancer has an enormous societal and health care impact and, due to the aging population, will become increasingly common. Given that the mean age of Veterans is 58, breast cancer will impact a significant number of Veterans in the next few years. The current Veteran population in the U.S. and Puerto Rico is approximately 26 million; of these, nearly 200,000 female Veterans will be diagnosed with breast cancer during their lifetimes. Reduction in mortality from this disease is an important goal. Breast cancer mortality is generally due to the occurrence of local and distant spread or metastasis. Our laboratory has identified several determinants of breast cancer metastasis. It is well established that the cyclooxygenase-2 (COX-2) enzyme is highly expressed and is associated with a poor prognosis in breast, colon, prostate and other malignancies. Recent concerns regarding the cardiac toxicity of COX-2 inhibitors prompted us to examine other approaches to therapeutically target the COX-2 pathway. We reasoned that preventing downstream signaling through the COX-2 product PGE2 would also be beneficial; however that hypothesis was only partially confirmed. We showed that breast tumors express all four known PGE receptors (EP1-4) and that antagonizing EP4 is beneficial whereas antagonism of EP1 actually promotes metastasis. Thus, the EP1 receptor appears to function as a metastasis suppressor. We will examine these relationships further in order to identify how to restore the balance between protective and anti-protective EP receptor function to reduce mortality from metastatic breast cancer.